The invention relates to power tools and, more particularly, to a spindle lock system for a power tool.
A typical electric machine, such as a rotary power tool, includes a housing, a motor supported by the housing and connectable to a power source to operate the motor, and a spindle rotatably supported by the housing and selectively driven by the motor. A tool holder, such as a chuck, is mounted on the forward end of the spindle, and a tool element, such as, for example, a drill bit, is mounted in the chuck for rotation with the chuck and with the spindle to operate on a workpiece.
To assist the operator in removing and/or supporting the tool element in the tool holder, the power tool may include a spindle lock for preventing rotation of the spindle relative to the housing when a force is applied by the operator to the tool holder to remove the tool element. Without the spindle lock, such a force would tend to rotate the spindle relative to the housing. The spindle lock may be a manually-operated spindle lock, in which the operator engages a lock member against the spindle to prevent rotation of the spindle, or an automatic spindle lock, which operates when a force is applied by the operator to the tool holder.
There are several different types of automatic spindle locks. One type of automatic spindle lock includes a plurality of wedge rollers which are forced into wedging engagement with corresponding wedge surfaces when a force is applied by the operator to the tool holder. Another type of automatic spindle lock includes inter-engaging toothed members, such as a fixed internally-toothed gear and a movable toothed member supported on the spindle for rotation with the spindle and for movement relative to the spindle to a locked position in which the teeth engage to prevent rotation of the spindle.
To accommodate such automatic spindle locks, some rotational play or movement may be provided between the spindle and the driving engagement with the motor. The spindle lock operates (is engaged and disengaged) within this xe2x80x9cfree anglexe2x80x9d of rotation between the spindle and the driving engagement of the motor.
One independent problem with the above-identified automatic spindle locks is that, when the motor is switched from an operating condition, in which the spindle is rotatably driven, to a non-operating condition, the inertia of the still-rotating spindle (and tool holder and/or supported tool element) causes the automatic spindle lock to engage to stop the rotation of the spindle relative to the motor within the free angle of rotation between the spindle and the motor. The engagement of the spindle lock can be sudden, causing an impact in the components of the spindle lock, resulting in noise (a big xe2x80x9cclunkxe2x80x9d) and, potentially, damage to the components.
This problem is increased the greater the inertia acting on the spindle (i.e., with larger tool elements, such as hole saws). With the high-inertia tool elements, the spindle may rebound from the impact (of the spindle lock engaging), rotate in the opposite direction (through the free angle of rotation) and impact the driving engagement with the motor, and rebound (in the forward direction) to re-engage the spindle lock. Such repeated impacts on the spindle lock and between the spindle and the driving engagement of the motor causes a xe2x80x9cchatteringxe2x80x9d phenomenon (multiple noises) after the initial impact and big xe2x80x9cclunkxe2x80x9d.
Another independent problem with existing power tools is that, when the motor is switched from the operating condition to the non-operating condition, a braking force may be applied to the motor while the spindle (under the force of the inertia of the spindle (and tool holder and/or supported tool element) continues to rotate through the free angle. The braking of the motor (coupled with the continued rotation of the spindle) causes the automatic spindle lock to engage resulting in noise (a big xe2x80x9cclunkxe2x80x9d and/or xe2x80x9cchatteringxe2x80x9d) and, potentially, damage to the components.
The braking force applied to the motor can result from dynamic braking of the motor, such as by the operation of a dynamic braking circuit or as results in the operation (stopping) of a cordless (battery-powered) power tool. In other words, when the motor is stopped, the difference between the force rotating the spindle (the inertia of the spindle (and tool holder and/or supported tool element) and the force stopping the motor (i.e., whether the motor coasts or is braked) causes the automatic spindle lock to engage. The greater difference in these oppositely acting forces, the greater the impact(s) (a big xe2x80x9cclunkxe2x80x9d and/or xe2x80x9cchatteringxe2x80x9d) when the spindle lock engages.
The present invention provides a power tool and a spindle lock system which substantially alleviates one or more of the above-described and other problems with existing power tools and spindle locks. In some aspects, the invention provides a spindle lock including a spring element for delaying operation of the spindle lock and a detent arrangement defining a position corresponding to a run position of the power tool and a position corresponding to a locked position of the spindle lock. In one rotational direction (i.e., the forward direction), a projection is positioned in first recess to provide an unlocked position and in a second recess to provide the locked position. In the opposite rotational direction (i.e., the reverse direction), the projection is positioned in the second recess to provide the unlocked position and in the first recess to provide the locked position.
In some aspects, the invention provides a spindle lock including a spring element which applies substantially equal spring force to delay the operation of the spindle lock when the spindle is rotated in the forward direction or in the reverse direction. In some aspects, the invention provides two spring members which cooperate to apply the substantially equal force to delay the operation of the spindle lock when the spindle is rotated in the forward direction or in the reverse direction.
In some aspects, the spindle lock is a wedge roller type spindle lock. In some aspects, the invention provides a spindle lock including a synchronization member for synchronizing the engagement of the locking members and the locking surfaces of the spindle lock. In some aspects, the invention provides a spindle lock having an aligning member for aligning the axis of the wedge roller with the axis of the spindle and maintaining such an alignment. In some aspects, the invention provides a battery-powered tool including a spindle lock.
One independent advantage of the present invention is that stopping of the motor and automatic locking of the spindle can be done quietly without producing the impact or xe2x80x9cclunkxe2x80x9d accompanied by the sudden engagement of the spindle lock. The resilient force of the spring element of the spindle rotation controlling structure buffers and controls the rotation of the spindle caused by the inertia of the spindle (and tool holder and/or supported tool element). This resilient force also buffers and controls the inertia of the spindle when there is little or no relative rotation between the spindle and the driving engagement with the motor.
Another independent advantage of the present invention is that, even if the inertia of the spindle, tool holder and supported tool element is greater than the resilient force of the spring element of the spindle rotation controlling structure (such that the rotation of the spindle does not stop immediately upon the initial engagement of the spindle lock), the spring element buffers and controls the rotation of the spindle to dissipate the rotating energy of the spindle without the repeated impacts and rebounds or xe2x80x9cchatteringxe2x80x9d, providing a more quiet stopping of the spindle.
A further independent advantage of the present invention is that, even when the motor is braked at stopping, such as by the operation of a braking circuit or in the operation of a cordless power tool, the spindle lock and the spring element of the spindle rotation controlling structure will quietly stop the rotation of the spindle, tool holder and tool element.
Other independent features and independent advantages of the present invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings.